1. Field of the Invention
The present invention relates to an embroidery data producing apparatus for an embroidery machine, and more particularly, to an embroidery data producing apparatus for producing the embroidery data which represents stitch positions on a pair of facing outlines extending in an embroidery executing direction.
2. Description of Related Art
An embroidery machine for embroidering a predetermined pattern, such as a one point mark, comprises a needle bar driving mechanism for reciprocating a needle bar which includes a needle at an end portion thereof, a horizontal moving mechanism for moving a work fabric in a horizontal plane, and a control device for controlling the needle bar driving mechanism and the horizontal moving mechanism. The control device controls the needle bar driving mechanism and the horizontal moving mechanism such that the needle can drop into each stitch position in sequence based on the embroidery data which represents stitch positions corresponding to the predetermined pattern. The embroidery data which represents stitch positions is automatically made by the embroidery data producing apparatus.
The embroidery data producing apparatus comprises a microcomputer, input devices such as an image scanner or a keyboard, and an external memory device. The external memory device stores the pattern data which represents an outline of the pattern, i.e., outline of an area which is filled with embroidery stitches. The microcomputer reads the pattern data stored in the external memory device and produces the embroidery data by calculating each stitch position based on the pattern data.
As shown in FIG. 9, in the case where the shape of an embroidery pattern 1 is a circle, the pattern data is made with the coordinate values which represent a plurality of points on an outer line 2 and an inner line 3 which outline the circle. First, the embroidery data producing apparatus calculates the coordinates values representative of the center point O of the pattern 1. The embroidery data producing apparatus then radially draws straight lines, the number of which is set according to a predetermined thread density, from the center point O. The embroidery data producing apparatus calculates the coordinate values which represent points of intersection of these straight lines alternating between the outer line 2 and the inner line 3 to represent stitch positions. During sewing, the needle follows the sequence between the outer line 2 and the inner line 3 of the pattern 1, for example in the clockwise direction, on the work fabric based on the embroidery data. As the result, the inside of the pattern 1 is filled with the embroidery stitches as shown.
The above-mentioned embroidery data producing apparatus produces the embroidery data for forming embroidery stitches which connect in sequence a pair of outlines. The embroidery stitches which are formed based on the embroidery data are substantially at a right angle to the pattern outline or a line parallel thereto defining the embroidery executing direction. The embroidery executing direction is the direction in which the pattern is formed, for example, from right to left, from top to bottom, clockwise or counterclockwise. A line commencing at a mid-point between the pair of outlines, adjacent the first stitch position, and passing parallel (to and through the midpoints) between the pair of outlines to a point adjacent a last stitch position defines an axis of the embroidery executing direction.
However, when embroidery stitches are formed at a substantially right angle with the axis of the embroidery executing direction (hereinafter called embroidery execution direction) and the interval between a pair of the outlines is narrow, the length of the stitches become very short. Because of this, the work fabric wrinkles and the stitches are denser or more compact and the lower thread may be pulled out through the upper surface of the work fabric. Therefore, neat embroidery stitches are not formed.